Quote:
Originally Posted by Perdu
Larry,
I'm just having problems visualizing a free sprung balance if you could say some more? :
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Gary,
I don't want to write a book, but let me see if I can say a few words.. (My apologies to all watchmakers)
1. On a Free-sprung balance, the balance wheel and hairspring ride on jewels at each end of the staff (axle), and the hairspring itself is attached to the inside of the wheel at the axle; the other end of the hairspring is attached (anchored) to the bridge (a stud screw holds it in place there). That's it...it's not attached any place else. On a Rolex, the speed of the hairspring is adjusted by the micro-stella screws and weights on the outside of the balance wheel... Screw the weights in closer, or out further to change the inertia/speed.
On a regulator balance, the wheel has the same axle, jewels, and pivots, and the hairspring is attached to the staff at the inside, but the other end of the hairspring is run through some pins (clamped) at the outside end to an eccentric screw. Regulation is made by taking the clamped end, turning the screw, and twisting the hairspring tighter, or looser to achieve a speed change.
2. The full balance bridge does make a difference.. First, Rolex uses a larger balance wheel than the Omega 1120/1128. The balance cock as used in the 1120/1128 (half bridge) extends halfway out into space to hold the balance pivot jewel and shock spring. After a shock or a bump, this hanging length of metal can vibrate the same way the ends of a tuning fork vibrate when hit. This half-bridge can only swing a moderate sized wheel because it swings (rotates) rapidly, so this piece of metal hanging out is also subject to the lateral forces caused by the mass of the wheel starting and stopping.. The half bridge can vibrate up and down, and laterally with the mass of the wheel.
The full balance bridge spans the entire distance and is anchored at both ends. The balance pivot jewel and shock system is placed in the middle. It cannot vibrate. It also allows Rolex to use a much larger balance wheel because, again, anchored at both ends, it cannot move laterally either.
(I'm not bashing the Omega 1120/1128, it's my favorite Omega movement. I'm just saying that from an engineering perspective, these points give the Rolex movement an edge)